Engineering Commons^™

Hermite Neural Network Correlation And Application, M. R. Mackenzie, K. Tieu

Faculty of Engineering - Papers (Archive)

A method for obtaining the correlation of two Hermite neural networks is developed. The method is based on the fact that a Hermite function is unchanged by the Fourier transform, which allows an expression for the correlation to be obtained directly from the network weights without the need for the Fourier transform. Comparative results with other neural network correlation methods are presented on simulated radar signals.

Accelerated Iterative Blind Deconvolution Of Still Images, Prashan Premaratne, M. Premaratne

Faculty of Engineering - Papers (Archive)

We propose an approach for blind deconvolution of still images with moderate noise contamination. The iterative technique is based on the general concepts of iterative techniques for blind deconvolution. The ill-convergence problem associated with most of the iterative techniques is circumvented in our approach using zero-sheet separation techniques. This technique can handle real images blurred by complex point spread functions (PSF), which is a common imaging problem, with blur signal-to-noise ratios (BSNR) of 70 dB and above for PSF of size 32/spl times/32 and larger. The technique performs much better for PSF of smaller sizes with low BSNR around 30 …

Two-Phase (Air And Water) Flow Through Rock Joints: Analytical And Experimental Study, Buddhima Indraratna, P. G. Ranjith, J. R. Price, W. Gale

Faculty of Engineering - Papers (Archive)

This research study deals with the characterization of two-phase flow in a fractured rock mass. A comprehensive mathematical model with which to predict the quantity of each flow component in a single joint is developed. A joint with two parallel walls filled with layers of water and air (stratified) is analyzed. The effects of mechanical deformation of the joint, the compressibility of fluids, the solubility of air in water, and the phase change between fluids have been taken into account to develop analytical expressions which describe the behavior at the air–water interface. The model was calibrated using a newly designed …

Magnetospectroscopy Of Be In Gaas , R. A. Lewis, Y. Wang, M. Henini

Faculty of Engineering - Papers (Archive)

Far-infrared absorption measurements have been made of the Lyman series of the acceptor Be in GaAs up to magnetic fields of 30 T, supplemented by photothermal ionization spectroscopy measurements to 6 T. The results confirm and greatly extend previous work and reveal several phenomena. The strongest component of the G line moves to higher energies and increases in intensity with field. Around 20 T the field dependence of the transition displays a marked kink. At higher fields the dependence of energy on field is linear. This behavior is attributed to unresolved components that change in relative intensity with field and …

A Comparison Of Ag And Ag-Alloy Sheathed Bi-2223 Tapes, Hua-Kun Liu, Z. M. Zhang, R. Zeng, J. Horvat, M. Apperley

Faculty of Engineering - Papers (Archive)

Ag and Ag-alloy sheathed Bi-2223 tapes were fabricated by a powder-in-tube technique with different configurations of the precursor and restack sheath materials: Ag, AgAu7 wt%, AgSb0.6 wt%, AgMg0.2 wt%. Analysis of the I/sub c/ and volume fractions of the Bi-2223, Bi-2212, Bi-2201 and Bi-3221 phases indicated that volume fractions of Bi-2223>90%, Bi-2212/spl sim/5%, Bi-2201/spl sim/0% and Bi-3221<2%, normally result in tapes with the highest I/sub c/. The mechanical properties of the tapes revealed consistent results. Generally, the harder the sheath material, the higher tolerance to the bending strain and higher the tensile strength of the tape. The sequence of the alloys' hardness from highest to lowest was AgMg0.2 wt%, AgSb0.6 wt%, AgAu7 wt% or Ag.

Characterization Of Thermal Conductivity And Mechanical Properties Of Ag-Alloy Sheathed Bi(Pb)-Sr-Ca-Cu-O Superconductor Tape, S. H. Jang, J. H. Lim, J. K. Kim, B. K. Ji, J. Jo, W. Nah, J. S. Volf, Hua-Kun Liu, M. Apperley

Faculty of Engineering - Papers (Archive)

We evaluated the effect of alloying additions to Ag on thermal conductivity and mechanical properties of Ag-alloy sheathed Bi-2223 (BSCCO) superconductor tape. The tapes were made with combinations of Ag alloys such as Ag-Mg, Ag-Sb, and Ag-Au for inner and outer sheath. Thermal conductivity of the tapes was evaluated by using thermal integral method at 10-120 K. It was observed that the addition of alloys reduced remarkably thermal conductivity and improved mechanical strength. The thermal conductivity for Ag-Mg, Ag-Sb, and Ag-Au at 40 K was measured to be 411.4, 142.3, and 109.7 W/(m/spl middot/K), respectively, which is approximately 2 to …

Modelling Of Prefabricated Vertical Drains In Soft Clay And Evaluation Of Their Effectiveness In Practice, Buddhima Indraratna, C. Bamunawita, I. Redana, G. Mcintosh

Faculty of Engineering - Papers (Archive)

Prefabricated vertical band drains are rapidly increasing in popularity as one of the most cost-effective soft clay improvement techniques worldwide. Nevertheless, problems caused during installation (such as the smear effect), drain clogging and well resistance of long drains contribute to retarded pore pressure dissipation, making these drains less effective in the field. This leads to reduced settlement compared with that which would be expected from ideal drains. This paper is an attempt to discuss, comprehensively, the modelling aspects of prefabricated vertical drains and to interpret the actual field data measured in a number of case studies that demonstrate their advantages …

Investigating Localized Degradation Of Organic Coatings, L. V. Philippe, G. W. Walter, S. B. Lyon

Faculty of Engineering - Papers (Archive)

The degradation of polyester coil-coated galvanized steel was compared using both conventional (macroscopic) and localized electrochemical impedance techniques on the same specimen and within a time interval (hours) much shorter than the total immersion period (days). Specimens containing a central 250 μm laser-ablated defect in the organic coating layer were immersed in a 10 mM NaCl solution for up to 30 days. The local multifrequency impedance was determined by placing a novel impedance probe, either directly above the coating defect or above an area of intact coating. In addition, single frequency impedance mapping of the specimen surface was carried out …

Induced Charge-Density Oscillation Under A Quantizing Magnetic Field And Intense Terahertz Radiation , M. Fujita, T. Toyoda, J. C. Cao, C. Zhang

Faculty of Engineering - Papers (Archive)

The time-dependent Schro¨dinger equation for a two-dimensional electron gas in a strong magnetic field and an intense terahertz laser field is solved by constructing unitary transformations. We calculate the chargedensity fluctuation under a weak probing potential. It is found that the induced charge density oscillates rapidly in time with two characteristic frequencies, the cyclotron frequency and the laser frequency.

Magnetic Shielding In Mgb2/Fe Superconducting Wires, J. Horvat, Saeid Soltanian, Xiaolin Wang, S. X. Dou

Faculty of Engineering - Papers (Archive)

Transport critical current (I/sub c/) was measured for MgB/sub 2//Fe round wires, with the magnetic field oriented perpendicular to the wire and parallel to it. Measurements were made on a wire with a pure MgB/sub 2/ core and another wire where the MgB/sub 2/ core was doped with nano-size SiC. This doping strongly improved the vortex pinning in MgB/sub 2/. The field dependence of I/sub c/ was strongly improved due to the presence of the iron sheath. At 30 K, I/sub c/ did not depend on the field for fields between 0.09 and 0.7 T. At lower temperatures, I/sub c/ …

Let Dependence Of The Charge Collection Efficiency Of Silicon Microdosimeters, I. Cornelius, Anatoly B. Rosenfeld, R. Siegele, D. D. Cohen

Faculty of Engineering - Papers (Archive)

A heavy ion microprobe was used to conduct ion beam induced charge (IBIC) collection imaging of silicon microdosimeters. The GEANT4 Monte Carlo toolkit was used to simulate these measurements to calculate ion energy loss in the device overlayer and energy deposition in the device sensitive volume. A comparison between experimental and theoretical results facilitated the calculation of charge collection efficiency profiles for several ions.

Calculation Of The Temperature Dependent Ac Susceptibility Of Superconducting Disks, M. J. Qin, G. Li, Hua-Kun Liu, S. X. Dou

Faculty of Engineering - Papers (Archive)

The temperature dependent complex AC susceptibilities of high temperature superconducting disks in perpendicular AC magnetic fields (in absence of DC magnetic field) have been calculated from first principles. The temperature dependent AC susceptibilities for different AC field amplitudes, AC field frequencies, reduced pinning potential, and sample thickness have been derived, which demonstrate many features different from what has been observed in the configuration of infinite long slab or cylinder under a parallel-applied AC field. The results of such a realistic configuration of finite-thickness samples in perpendicular fields can be compared directly to the experimental results.

Magnetic Hysteresis And Relaxation In Bi2212 Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, G. D. Gu, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt

Faculty of Engineering - Papers (Archive)

Magnetic hysteresis and magnetic relaxation measurements have been performed to study vortex pinning behaviors for pure, Fe doped and heavily Pb doped Bi2212 single crystals. Unlike pure and Fe doped Bi2212 crystals, heavily Pb doped crystal showed strong vortex pinning behavior. We interpret the strong pinning in heavily Pb doped Bi2212 single crystals as arising from the improved Josephson coupling in Bi2212 single crystal after heavy Pb doping. In heavily Pb doped single Bi2212 crystals, H/sub dis/(T) was observed to decrease with increasing T. Here, H/sub dis/(T) is an order-disorder field that separates a weakly elastically disordered vortex lattice from …

Effect Of Grain Size And Doping Level Of Sic On The Superconductivity And Critical Current Density In Mgb/Sub 2/ Superconductor, Saeid Soltanian, Xiaolin Wang, J. Horvat, M. J. Qin, Hua-Kun Liu, P. R. Munroe, S. X. Dou

Faculty of Engineering - Papers (Archive)

SiC doped MgB/sub 2/ polycrystalline samples were fabricated by in-situ reaction using different grain sizes (20 nm, 100 nm, and 37 /spl mu/m) of SiC and different doping levels (0, 8, 10, 12, 15 wt%). Phases, microstructures, superconductivity, critical current density and flux pinning have been systematically investigated using XRD, SEM, TEM, and magnetic measurements. Results show that grain sizes of the starting precursors of SiC have a strong effect on the critical current density and its field dependence. The smaller the SiC grains are, the better the J/sub c/ field performance is. Significant enhancement of J/sub c/ and the …

Transport Critical Current Density In Fe-Sheathed Nano-Sic Doped Mgb/Sub 2/ Wires, S X. Dou, J. Horvat, Saeid Soltanian, Xiaolin Wang, M. J. Qin, S. H. Zhou, Hua-Kun Liu, P. G. Munroe

Faculty of Engineering - Papers (Archive)

The nano-SiC doped MgB/sub 2//Fe wires were fabricated using a powder-in-tube method and an in-situ reaction process. The depression of T/sub c/ with increasing SiC doping level remained rather small due to the counterbalanced effect of Si and C co-doping. The high level SiC co-doping allowed creation of the intra-grain defects and nano-inclusions, which act as effective pinning centers, resulting in a substantial enhancement in the J/sub c/(H) performance. The transport J/sub c/ for all the wires is comparable to the magnetic J/sub c/ at higher fields despite the low density of the samples and percolative nature of current. The …

A Non-Destructive, Non-Contact, Quality Test Of Critical Current For Ag-Biscco Tape, A. Gandini, R. Weinstein, D. Parks, R. Sawh, S. X. Dou

Faculty of Engineering - Papers (Archive)

An accurate noncontact method of characterizing Ag-BiSCCO tape is reported, using the trapped field, B/sub t/, of a field-cooled tape. The dimensions of the tape make it possible to calculate in closed form a very simple expression, relating trapped field to transport current. Short lengths of tape, 4 cm, are used to experimentally confirm the model. The model applies to any length of tape for which length is greater than 5 times the tape width. A schematic of a proposed test apparatus is presented which should permit on-line testing for magnitude of the current, and for cracks, while the tape …

On The Limiting Mechanism Of Irradiation Enhancement Of I/Sub C/, A. Gandini, R. Weinstein, D. Parks, R. Sawh, S. X. Dou

Faculty of Engineering - Papers (Archive)

Irradiation may significantly increase I/sub c/ in HTS. A systematic pattern occurs: R=I/sub c/(afterirr.)/I/sub c/(beforeirr.) increases at low defect density, d. It reaches a peak, and then it falls below 1 at high d. The pinning center mechanism, which causes R to increase, has been extensively studied. The falloff in R has not. It has been considered a secondary effect. Here, we will show that the fall-off plays an important role in determining the maximum I/sub c/ enhancement achievable. A phenomenological model to describe the R-vs.-d curve, over the entire d range, is proposed. The idea is that R is …

Effects Of The Field Dependent J/Sub C/ On The Vertical Levitation Force Between A Superconductor And A Magnet, G. Li, M. J. Qin, Hua-Kun Liu, S. X. Dou

Faculty of Engineering - Papers (Archive)

The vertical levitation force between a superconductor disk (SC) and a permanent magnet disk (PM) has been calculated from first principles using different J/sub c/(B) relationships of the magnetic field. Based upon the first principles, the current distribution inside the SC induced by the applied inhomogeneous magnetic field generated by the PM and the field profiles have been calculated with a power law E /spl sim/ J relationship: E(J) = E/sub c/(J/J/sub c/(B))/sup n/. The levitation force is highly hysteretic for the approaching and the retreating branches. The saturated current value, magnetization, and levitation force are found to depend strongly …

Readout Of Lyso Using A New Silicon Photodetector For Positron Emission Tomography, M. L. Lerch, R. Ward, Philip E. Simmonds, V. L. Perevertailo, S. R. Meikle, G. N. Taylor, Anatoly B. Rosenfeld

Faculty of Engineering - Papers (Archive)

This article focuses on the characterisation of three versions of a custom designed silicon photodetector using nuclear spectroscopy techniques. Room temperature gamma ray spectroscopy experiments have been performed using an LYSO excited by /sup 137/Cs and /sup 22/Na sources and read out by the new photodiodes. We have measured an energy resolution of 13.1% FWHM for the 511 keV gamma rays from a /sup 22/Na source and 11.2% FWHM for the 662 keV gamma rays from a /sup 137/Cs source. This is one of the best ever-reported energy resolutions for a lutetium based scintillator crystal read out by a silicon …

Verification Of Monte Carlo Calculations In Fast Neutron Therapy Using Silicon Microdosimetry, I. Cornelius, Anatoly B. Rosenfeld

Faculty of Engineering - Papers (Archive)

Silicon microdosimetry measurements in fast neutron therapy were simulated using the GEANT4 Monte Carlo toolkit. The possibility of using silicon microdosimeters for verification of Monte Carlo based treatment planning systems in hadron therapy is demonstrated.

Performance Evaluation Of A Multipinhole Small Animal Spect System, S. R. Meikle, P. Kench, R. Wojcik, M. F. Smith, A. G. Weisenberger, S. Majewski, M. L. Lerch, Anatoly B. Rosenfeld

Faculty of Engineering - Papers (Archive)

We have designed and constructed a small animal SPECT system based on compact, high resolution detectors and multipinhole apertures. The scanner is currently configured with two detectors mounted on a rotating gantry. Each detector comprises a NaI(Tl) crystal array (1/spl times/1/spl times/5 mm elements), a 12 cm diameter position-sensitive photomultiplier tube (Hamamatsu R3292) and a tungsten aperture with 1 or more pinholes. In this study, we performed phantom experiments to characterise the planar and tomographic performance of the scanner. Intrinsic resolution measured with a highly collimated /sup 99m/Tc point source stepped across the detector face was 1.0 /spl plusmn/ 0;.1 …

Effects Of Fission-Fragment Damage On Vortex Dimensionality In Silver-Sheathed Bi2sr2ca2cu3ox Tapes, D. G. Marinaro, J. Horvat, S X. Dou

Faculty of Engineering - Papers (Archive)

We report on the vortex dimensionality of uranium-doped Ag/Bi2223 tapes, before and after irradiation to a thermal-neutron fluence. The effective activation energies, as a function of current density and applied field, were calculated from dynamic magnetization relaxation measurements. A dimensional crossover from a three-dimensional (3D) elastic creep regime to a 2D plastic creep was observed in the nonirradiated tape at an applied magnetic field µ0Hcr[approximate]0.37 T, with an associated change in the flux hop velocity and temperature dependence. After the introduction of the fission-fragment damage by irradiation, a shift in the crossover to µ0Hcr[approximate]0.65 T was observed. These results indicate …

Superconductivity, Critical Current Density, And Flux Pinning In Mgb2–X(Sic)X/2 Superconductor After Sic Nanoparticle Doping, S X. Dou, A. V. Pan, S. Zhou, M. Ionescu, Xiaolin Wang, J. Horvat, Hua-Kun Liu, P. R. Munroe

Faculty of Engineering - Papers (Archive)

We investigated the effect of SiC nanoparticle doping on the crystal lattice structure, critical temperature Tc, critical current density Jc, and flux pinning in MgB2 superconductor. A series of MgB2–x(SiC)x/2 samples with x = 0–1.0 were fabricated using an in situ reaction process. The contraction of the lattice and depression of Tc with increasing SiC doping level remained rather small most likely due to the counterbalancing effect of Si and C co-doping. The high level Si and C co-doping allowed the creation of intragrain defects and highly dispersed nanoinclusions within the grains which can act as effective pinning centers for …

Intense Vortex Pinning Enhanced By Semicrystalline Defect Traps In Self-Aligned Nanostructured Mgb2, S. Li, T. White, K. Laursen, T. T. Tan, C. Q. Sun, Z. L. Dong, Y. Li, S. H. Zho, J. Horvat, S. X. Dou

Faculty of Engineering - Papers (Archive)

In this work, we report the discovery of a vortex pinning source: semicrystalline defect wells in self-aligned nanostructured MgB2. It is demonstrated that these aperiodic regions trap numerous crystal defects migrating along nanodomain boundaries during self-alignment and act as intense vortex pinning centers that significantly enhance the high-field performance of MgB2. This suggests that the density of trapped defects in the wells is much greater than that found in other vortex pinning sources.

Effect Of Carbon Nanotube Doping On Critical Current Density Of Mgb2 Superconductor, S X. Dou, W. K. Yeoh, J. Horvat, M. Ionescu

Faculty of Engineering - Papers (Archive)

The effect of doping MgB2 with carbon nanotubes on transition temperature, lattice parameters, critical current density and flux pinning was studied for MgB2–xCx with x = 0, 0.05, 0.1, 0.2, and 0.3. The carbon substitution for B was found to enhance Jc in magnetic fields but depress Tc. The depression of Tc, which is caused by the carbon substitution for B, increases with an increasing doping level, sintering temperature, and duration. By controlling the extent of the substitution and addition of carbon nanotubes we can achieve the optimal improvement on critical current density and flux pinning in magnetic fields while …

Mosfet Dosimetry For Microbeam Radiation Therapy At The European Synchrotron Radiation Facility, E. Brauer-Krisch, A. Bravin, M. L. Lerch, Anatoly B. Rosenfeld, J. Stepanek, M. Di Michiel, J. A. Laissue

Faculty of Engineering - Papers (Archive)

Preclinical experiments are carried out with ~20–30 μm wide, ~10 mm high parallel microbeams of hard, broad-‘‘white’’-spectrum x rays (~50–600 keV) to investigate microbeam radiation therapy (MRT) of brain tumors in infants for whom other kinds of radiotherapy are inadequate and/or unsafe. Novel physical microdosimetry (implemented with MOSFET chips in the ‘‘edge-on’’ mode) and Monte Carlo computer-simulated dosimetry are described here for selected points in the peak and valley regions of a microbeam-irradiated tissue-equivalent phantom. Such microbeam irradiation causes minimal damage to normal tissues, possible because of rapid repair of their microscopic lesions. Radiation damage from an array of parallel …

Dip Effect In Ac Susceptibility Due To Surface Barrier With Flux Creep, X. Leng, Shichao Ding, Y. Liu, Z. H. Wang, Hua-Kun Liu, S. X. Dou

Faculty of Engineering - Papers (Archive)

A model is proposed to describe the effect of surface barrier (SB) on ac susceptibility (ACS) and a different kind of dip effect ~DE! in ACS is observed. Simulation based on this model with flux creep reveals two dips in ACS curve, one at temperature Td8 in real part x8 and the other at temperature Td9 in imaginary part x9. These two dips are different from the ones resulting from the peak effect in critical current density jc , where the dips in x8 and x9 occur at the same temperature Tp . The DE is also characterized by a …

Effect Of Sample Size On The Magnetic Critical Current Density In Nano-Sic Doped Mgb2 Superconductors, Saeid Soltanian, M. J. Qin, S. Keshavarzi, Xiaolin Wang, S. X. Dou

Faculty of Engineering - Papers (Archive)

The effect of sample size on the critical current density and the flux pinning of pure and SiC doped MgB2 bulk samples has been investigated. At high fields a systematic degradation of magnetic Jc and Hirr was observed as the sample size decreased. However, Jc remarkably increased on decreasing the sample volume at low magnetic fields below 1 T. The SiC doped samples show less sample size effect than the pure samples, indicating a larger n factor and therefore a stronger pinning effect due to SiC doping. Hirr was observed to decrease as a logarithmic function of the sample volume, …

A Review Of Methods For Predicting Bomb Blast Effects On Buildings, Alexander Remennikov

Faculty of Engineering - Papers (Archive)

In recent years, the explosive devices have become the weapon of choice for the majority of terrorist attacks. Such factors as the accessibility of information on the construction of bomb devices, relative ease of manufacturing, mobility and portability, coupled with significant property damage and injuries, are responsible for significant increase in bomb attacks all over the world. In most of cases, structural damage and the glass hazard have been major contributors to death and injury for the targeted buildings. Following the events of September 11, 2001, the so-called “icon buildings” are perceived to be attractive targets for possible terrorist attacks. …

Hook Crack In Electric Resistance Welding Line Pipe Steel, Sima Aminorroaya-Yamini, Hossein Edris, Mehrdad Fatahi

Australian Institute for Innovative Materials - Papers

One of the production methods for API line pipe steel is electric resistance welding (ERW). This kind of pipes is encountered with hook crack which is one of the defects that is observed in the upset zone of ERW pipes, detecting by ultrasonic inspection. Hook crack is a small crack following the weld flow lines and if severe enough, opened up at the pipe surface. These defects were commonly associated with sulphide stringers and non metallic oxide inclusions.

In this research, welds containing hook cracks were obtained from Ahvaz pipe making factory. Scanning electron microscope (SEM) examination showed that all …